L-type voltage dependent calcium channels (VDCCs) are critical components in the regulation of cardiac function. The kinetic characteristics of these channels, which are important in controlling heart rate and force of contraction, are defined by the primary sequence of the four subunits that make up each channel. The objectives of this proposal are to determine the intracardiac distribution of the three beta subunits of L-type VDCCs present in the heart, and to determine the role of the beta subunit in the regulation of the L-type VDCC present in working myocardium. The specific aims are; 1) to isolate and characterize murine cDNA and genomic clones from the beta2 and beta3 subunit genes, 2) to determine the distribution of the beta1, beta2 and beta3 subunits by in situ hybridization and immunohistochemical detection in heart sections. 3) use gene targeting, to produce a mouse that lacks the beta subunit that is predominantly expressed in working myocardium, and 4) to characterize the effect of this beta null mutation on the L-type VDCC of cardiac myocytes and on the physiology of the intact animal. Specifically modified beta subunits will be introduced into either beta null myocytes or beta null animals to determine their effect on the regulation of the cardiac L-type VDCC.